Light leaf spot is the main reason for the disappointing performance of many oilseed rape crops across the country this season, according to Agrii OSR specialist Philip Marr.

Although crops have looked extremely well, few have lived up to expectations, and Mr Marr has found LLS infections causing yield losses of 30-50%, through a combination of small seeds and premature pod opening.

“Verticillium is being blamed for disappointing yields by some,” he said. “But this season has seen some of the lowest levels of verticillium infection in recent years.

“In complete contrast, light leaf spot has become more and more obvious on a national scale as the season has gone on.

“From widespread leaf spotting as the weather warmed up in the spring, it has progressed into the most severe stem blotching I’ve ever seen on susceptible varieties, coupled with serious pod lesions in many crops.”

See also: Harvest round-up – Oilseed rape yields disappoint.

Yield losses had been severe in varieties with poor disease resistance ratings, added Mr Marr.

“One of the most resistant varieties in our Brotherton trials showed hardly any signs of infection and went on to produce over 5.5t/ha.

“Yet, alongside it we brought in barely 3.5t/ha from one of the most susceptible, which was riddled with stem and pod lesions.”

Varieties without pod shatter resistance appeared to be suffering more than most, resulting in high losses during harvest, he warned.

With a rapid decline in LLS sensitivity to triazoles, farmers had fewer opportunities to manage the disease, and should therefore select varieties with high resistance to LLS and pod shatter.

“It’s high time we took an altogether better-informed agronomic risk management approach to counter what has fast become the single biggest disease threat across such a large part of the country.”